If you want to see Alan "doing" Jeremy Sisto (well, you may not) you should take a look at the current "Suburgatory."
http://abc.go.com/watch/suburgatory/SH55126593/VD55241558/the-witch-of-east-chatswin
It's way better than Sisto doing Tudyk, IMHO.

orangewaxlion, I am in the strange position of having seen the movie, but not the trailer, so I don't know if/how Alan Tudyk's character comes up in the advertising. *I* wouldn't be worried to know the character's name, but since other people's spoiler sensitivities are of varying levels, I thought I should put a disclaimer. (Personally, I would have liked to have known that was Alan Tudyk going in - as it was, I was trying to figure out through the whole movie who the voice belonged to, and only found out when I saw the end credits.)